Excess of lensing amplitude in the Planck CMB power spectrum

Understand

Precise measurements of the Planck cosmic microwave background (CMB) angular power spectrum (APS) at small angles have stimulated accurate statistical analyses of the lensing amplitude parameter $A_{L}$.

• To confirm if it satisfies the value expected by the flat-$\Lambda$CDM concordance model, i.e.
• $A_{L} = 1$, we investigate the spectrum difference obtained as: the difference of the measured Planck CMB APS and the Planck best-fit $\Lambda$CDM APS model.
• To know if this residual spectrum corresponds to statistical noise or if it has a hiden signature that can be accounted for with a larger lensing amplitude $A_{L} > 1$, we apply the Ljung-Box statistical test and find, with high statistical significance, that the spectrum difference is not statistical noise.